Ceramic discharge lamp



g- 1969 w. .1. KNOCHEL ET AL 3,461,334

CERAMIC DISCHARGE LAMP Filed Feb. 27, 1967 II 20 I20 T 28 A t1 1 X z wl4 k\\\\\\ 22 27 "L50 5 I ll M 29 3| 26 Y m A;

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2 FIG. 6. FIG 7 WITNESSES: NVENTOR %m 9 71M William J. Knochel 0ndATTORNEY J I Bfiugh D. Fraser. W & fiaffw United States Patent m US. Cl.313-498 7 Claims ABSTRACT OF THE DISCLOSURE A ceramic discharge lamphaving an elongated tubular polycrystalline alumina envelope closed ateach end by an electrode carrying refractory metal closure member andhaving interposed through said ceramic envelope a ring-shaped refractorymetal starting electrode adjacent one of the electrodes carried by oneof the end closure members.

Background of the invention This invention relates to ceramic dischargedevices and more particularly to a ceramic discharge device employing arefractory metal starting electrode sealed through the ceramic arc tube.

In their conventional form ceramic discharge lamps employingpolycrystalline alumina arc tubes require a high voltage surge of from440 to 800 volts, or the use of a spark coil to initiate the discharge.This problem exists similarly in the conventional high-pressure,mercuryvapor, discharge lamp. In the high-pressure mercury type lamps,which generally employ a quartz arc tube, a press seal at each end ofthe arc tube seals off the interior. Through one of these press seals astarting electrode enters the discharge cavity in the same manner as theprimary arc sustaining electrodes. Unfortunately, with the narrowdiameters, or 4 inch internal diameter tubes, employed in the ceramicdischarge lamps a similar solution is not practical. Not only does sizepresent a problem, but additionally, the use of refractory metals forthe closure members in the form of disks or caps would require that thestarting electrode, should it enter through the end of the lamp, besufiiciently isolated from the electrically conductive end cap by meansof suitable insulating material.

Summary of the invention It is an object of the present invention toprovide a starting electrode for a ceramic discharge lamp.

Another object of the present invention is to provide a ceramicdischarge lamp wherein a starting electrode is provided that does notextend through either of the refractory metal end caps.

A further object of the present invention is the provision of a ceramicdischarge lamp having a starting electrode secured through the walls ofthe ceramic envelope.

The foregoing objects are accomplished in accordance with the presentinvention by employing, in a ceramic discharge lamp having an elongatedlight transmitting ceramic envelope confining a discharge sustainingfilling,

Patented Aug. 12, 1969 l Ce.

closure means sealed to and sealing off each end of said ceramicenvelope, and a discharge sustaining electrode and lead-in conductorsecured to each of said closure means, the improvement comprising; arefractory metal starting electrode sealed through the wall of saidenvelope adjacent one of said discharge sustaining electrodes. Theforegoing improvement is accomplished "by employing at least twoseparate tubular parts to form the ceramic discharge confining envelopewith a ring-shaped refractory metal starting electrode sealed betweenthe separate tubular parts and extending both internally and externallyof the envelope.

Brief description of the drawings The above-recited objects, and others,as well as many of the attendant advantages of the present inventionwill become more readily apparent and better understood as the followingdetailed description is considered in connection with the accompanyingdrawing, in which:

FIGURE 1 is a section view of a ceramic discharge device illustratingone form which the starting electrode of the present invention may take;

FIG. 2 is a sectional View taken along the line 11-11 of FIG. 1;

FIG. 3 is a sectional view of one end of a ceramic discharge deviceillustrating another embodiment of the present invention;

FIG. 4 is a sectional view of one end of a ceramic discharge deviceillustrating yet another embodiment of the present invention;

FIG. 5 is a sectional view taken along the line VV of FIG. 4;

FIG. 6 is a sectional view of one end of a ceramic discharge deviceillustrating yet another form which the starting electrode of thepresent invention may take; and

FIG. 7 is a sectional view of one end of the ceramic discharge deviceillustrating a still further embodiment of the present invention.

Description of the preferred embodiments Referring now in detail to thedrawings, wherein like reference characters represent like partsthroughout the several views, and more particularly to FIG. 1 there isshown a ceramic discharge device generally designated 10 illustratingone form or embodiment of the starting electrode of the presentinvention. The discharge lamp of the present invention generallyincludes a ceramic body in the form of a high density sinteredpolycrystalline alumina tube 12 hermetically sealed at each end by arefractory metal disk or end cap. For purposes of illustration an endcap 14 is employed to seal off one end of the polycrystalline aluminabody member 12 while a disk type hermetic seal is illustrated at theother end employing a refractory metal disk 16. When a disk type seal isemployed as illustrated by the disk 16 short polycrystalline aluminabackup rings are necessary as for example backup ring 18. Whencup-shaped caps are employed as for example end cap 14 the aluminabackup rings are unnecessary. In both the end cap construction and theend disk construction shown in FIG. 1 the hermetic seal is accomplishedby employing a ceramic sealing composition between the refractory metaldisk or cap and the polycrystalline alumina body member as illustratedat 20.

Although many suitable ceramic sealing compositions are known thesealing compositions disclosed in copending application Ser. No.562,016, filed June 30, 1966 for Sealing Compositions by R. B. Grekilaet al. and owned by the assignee of the present invention, arepreferred.

Each of the end closure members 14 and 16 are provided with a primary ordiscarge sustaining electrode and an electrical lead-in conductor tocarry current to the electrode. End cap 14 has mounted thereon a primaryelectrode 27 and refractory metal exhaust-and-fill tubula tion 21 servesas the lead-in conductor. At the other end, end disk 16 carries aprimary electrode 29 on its inner face and has a strap-type lead-inconductor 31 secured, as by brazing, to its outer face. Of course astrap-type lead-in conductor can be used with a cap shaped closuremember and refractory metal exhaust-and-fill tubulation can be used withthe disk-type closure member. Normally the arc tube will be sealed atboth ends with the disk-type or cap-type closure member and the use ofeach type in the FIG. 1 embodiment is primarily for purposes ofillustration.

As shown at the left-hand end of FIG. 1 the exhaustand-fill tubulationis secured centrally to the end cap or disk sealing off polycrystallinealumina arc tube 12. This exhaust-and-fill tubulation is generallysecured to the refractory metal end disk or cap by a titanium braze asillustrated at 22 and permits the exhausting of the sealed arc tube andthe subsequent filling thereof with a starting gas such as, for example,argon along with a discharge sustaining filling. The dischargesustaining filling may be any of the well known mercury-metal ormercury-metal halide arc sustaining fillings, such for example, asamalgam or sodium and mercury as indicated at 24. After the fillingprocedures, the tubulation 21 is pinched off to provide a hermetic sealat 26 thus completing the fabrication of an operative arc tube.

To obviate the requirement of a high voltage surge for example 440 to800 volts or for the use of a spark coil to initiate the discharge, thedischarge lamp of the present invention employs a starting electrode 28.The use of a starting electrode as herein contemplated requires that thepolycrystalline alumina envelope 12 be constructed of two separate parts12a and 12b and have secured therebetween, by the above-describedsealing compositions 20, the starting electrode 28 in the form of aniobium or tantalum ring. The ring may have welded thereto a tantalumstrap electrode 30 if desired. Although the part 12a of the ceramic tube12 must necessarily be a light transmitting ceramic such as for examplepolycrystalline alumina, the part 1211 need not necessarily be lighttransmissive but may be of some other ceramic as for example highdensity recrystallized alumina or other nontranslucent high-temperatureceramic since it is positioned behind the arc producing area between theelectrodes 27 and 29.

FIG. 3 illustrates another form which the starting elec trode of thepresent invention may take. In this embodiment, the stepped niobium ring38 has brazed thereto a tantalum ring 40.

The embodiments of FIGS. 4 and includes a stepped niobium or tantalumring 48 which may have a plurality of serrations or teeth 50 as an aidin directing the are between the primary electrode 29 and startingelectrode 48. The construction of the starting electrode 48 and itsassociation with the polycrystalline alumina envelope provides increasedstrength over the embodiments of FIGS. 1 and 3 in that all the sealsemploying the sealing compositions 2t) are circumferential in nature asopposed to the butt seals employed in the FIGS. 1 and 3 embodiments.

The embodiments of FIGS. 6 and 7 are similar in that they provide forcircumferential seals 20. The FIG. 6 starting electrode is constructedfrom a pair of flanged tantalum or niobium disks which are brazedtogether as at 56 to give the appearance of brazed together Us in crosssection. In the embodiment of FIG. 7, the starting electrode 68 is adouble flanged niobium or tantalum ring giving a T-shaped appearance incross-section and again provides for the circumferential seals at 20 asopposed to butt seals. In each of the embodiments of FIGS. 4, 6 and 7,the ceramic envelope 12 is hermetically sealed by a refractory metal endcap 14.

The operation of the starting electrode and the circuit therefor issubstantially identical with that employed in conventionalhigh-pressure, mercury-vapor discharge lamps. Of particular suitabilityis the starting circuit disclosed in copending application, Ser. No.379,109, now Patent No. 3,307,069, filed June 30, 1964 by H. D. Fraserand M. C. Unglert for Discharge Lamp which application is owned by theassignee of the present invention. As is the general practice an arc isinitially established between the starting electrode 28 and an adjacentoperating electrode 29 until sufiicient heat is generated within the arctube. At a preselected temperature, the starting electrode isdeactivated with the current previously flowing thereto now flowing tothe other operating or primary electrode 27 and the arc is accordinglytransferred from between the starting electrode 28 and operatingelectrode 29 to from between operating electrode 27 and operatingelectrode 29 without the requirement for an extremely high voltageapplication. The above-referred to copending application performs thisfunction by employing a self-resistance heated thermal electric elementwhich at rest is in electrical connection with the starting electrodebut upon reaching a predetermined heated level deforms to break contactwith the starting electrode circuit and establish contact with thecircuit of the other operating electrode.

Since numerous changes may be made in the abovedescribed apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings, shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A ceramic discharge lamp comprising:

(a) an elongated light transmitting ceramic envelope confining adischarge sustaining filling;

(b) closure means sealed to and sealing off each end of said ceramicenvelope,

(0) a discharge sustaining electrode and a lead-in conductor secured toeach of said closure means, said electrodes extending axially withinsaid envelope and said lead-in conductors extending exteriorly of thesealed lamp; and

(d) a refractory metal starting electrode sealed through the wall ofsaid envelope adjacent to and surrounding one of said dischargesustaining electrodes.

2. A ceramic discharge lamp according to claim 1 wherein said envelopecomprises two separate tubular parts and said starting electrodecomprises a refractory metal ring sealed between said tubular parts andextending both externally and internally of said envelope.

3. A ceramic discharge lamp according to claim 2 wherein said startingelectrode is a niobium ring having a tantalum strap secured to theinnermost edge thereof.

4. A ceramic discharge lamp according to claim 2 wherein said startingelectrode is a niobium ring having a tantalum ring secured theretoproximate its innermost edge.

5. A ceramic discharge lamp according to claim 2 wherein said startingelectrode is a stepped refractory metal ring sealed to one of saidtubular parts along its inner circumference and sealed to the outerperiphery of the other of said tubular parts.

6. A ceramic discharge lamp according to claim 2 wherein said refractorymetal starting electrode is a refractory metal ring having at least oneflange thereon,

said flange being sealed to the outer periphery of at least 2,449,1139/1948 Fruth 313-217 X one of said tubular parts and the inner endprojecting 2,508,114 5/1950 Jenne 313198 adjacent one of said dischargesustaining electrodes- 2,919,369 12/1959 Edgerton 313-498 X 7. A ceramicdischarge lamp according to claim 2 3 229 146 1 195 Linkroum 313 197 Xwherein said refractory metal ring has a plurality of 5 3,243,635 3/1966Louden et a1. 313 220 X serrations along its inner edge.

JAMES W. LAURENCE, Primary Examiner References Cited RAYMOND F HASSFELDA E UNITED STATES PATENTS ssstant Xammer 2,416,661 2/1947 Lawton 313-208X 10 2,416,927 3/1947 Kingdon et a1. 313198 X 313-216, 218, 220

